This invention relates to a relief valve which is especially useful to protect a power swivel as is used in oil and gas drilling operations.
With conventional power swivels, the hydraulic motor shaft seal can be blown out, due to accident or inexperience, in the event that the case drain hose becomes blocked or is disconnected or never attached. In the latter two cases, the drain is effectively blocked by the closed check valve in the hose quick-disconnect. A field shutdown results, and major labor is required to replace this inexpensive seal.
In many cases, hydraulic motor lip-type shaft seals used on power swivels have a much lower pressure rating than mechanical-type seals used in typical hydraulic pumps on these machines. In this case, if the pump fails before the motor, high case pressure fluid is sent through the common drain line to a perfectly good motor, thereby blowing a motor shaft seal. Major downtime results, due to the need to replace the seal, and further downtime and confusion can result due to difficulty in diagnosing the source of the problem, which is the pump, rather than the leaking motor.
A mechanism to protect the shaft seals of the motor and to alert personnel that a problem has occurred would be very desirable.
It is an object of this invention to provide a relief valve for a power swivel, to protect the seals.
It is a further object of this invention to provide a means to alert rig personnel that a problem has occurred with operation of the power swivel, which may endanger the seals.
According to one embodiment of the invention, a relief valve is installed to prevent pressure from rising high enough to blow the seal. When the relief valve relieves pressure, the hydraulic oil flow is directed perhaps 100 feet onto the rig floor below, to alert the rig personnel that something is wrong. This requirement also prevents the requirement for an additional long hose down to the power unit. The relief valve comprises a relief valve body, a valve seat insert for the body, a plunger valve element to seat against the insert, and a biasing means to urge the plunger against the valve seat.
The relief valve body has a first end and a second end and a generally longitudinally-extending passage extending into the valve body from the first end. The passage has an opening at the first end of the valve body and a bottom end which is spaced apart from the opening.
The valve seat insert is positioned in the generally longitudinally-extending passage of the relief valve body. The valve seat insert has a generally truncated cone-shaped valve seat surface which faces the bottom end of the generally longitudinally-extending passage in the relief valve body. The valve seat insert has a generally longitudinally-extending passage extending axially therethrough.
The plunger valve element has a first end and a second end and defines a generally truncated cone-shaped valve face positioned between the first end and the second end. The generally truncated cone-shaped valve face faces the first end of the valve element and forms a peripheral seal between an inside periphery of the valve seat surface and an outside periphery of the valve face when the relief valve is in a closed position.
A chamber is formed between the peripheral seal and the bottom end of the generally longitudinally extending passage. The relief valve body further defines at least one relief port which establishes a flow path between the chamber and an outside surface of the relief valve body to permit fluid flow through the longitudinally-extending passage of the valve seat insert and then through the at least one relief port when the relief valve is in an open position.
A biasing means is positioned in the chamber to bias the valve face against the valve seat surface and hold the relief valve in a normally closed position.
In a preferred embodiment, the valve is designed to hold pressure drop-tight, and if opened, to reclose drop-tight, unlike ordinary commercially available valves which were tried first. It is common knowledge in the hydraulics industry that such valves xe2x80x9cdribblexe2x80x9d constantly before opening at their relief setting, which is unacceptable in this application. Zero leakage can be tolerated dripping down onto the workers in normal operation, and the major xe2x80x9calarmxe2x80x9d flow may never actually occur. The preferred inventive valve acts simply as an insurance policy. It prevents expensive downtime resulting from an inadvertent simple error, and downtime of the swivel and confusing troubleshooting when the pump is actually at fault.